Shelly is just playing the game. I know that makes her a pretty lousy friend, but Jeff and Jordan would have thrown Shelly under the bus if it benefited their game. And they would have just said, "It's just about the game...." I think that they would have liked Shell and Adam in the jury because they were so "groupie-like" with Jeff and Jordan and I think J/J probably thought that even if they voted them out, Adam and Shelly would just think that J/J had to vote that way to keep peace in the house.
Don't get me wrong, I don't like Shelly. But intentional or not, she made a very strong move in her game and I wouldn't be surprised to see her go to the final two.